WASHINGTON – Longer droughts and more disastrous wildfires are killing freshwater fish in Arizona and other Southwestern states, threatening not just the fish but a sport worth hundreds of millions of dollars a year, a new report says.

The report last week by the National Wildlife Federation said climate change is to blame for the increasingly large wildfires and warmer winters that are dumping deadly amounts of ash into Southwestern rivers and reducing the snowpack that feeds those rivers.

Scientists have long known the potential effects of wildfires and droughts on fish populations, but it is important to note how climate change is exacerbating those problems, said Doug Inkley, a senior scientist at the federation, who co-authored the report.

“The climate change fueling these fires is actually the smoking gun,” Inkley said in a conference call Wednesday on the report.

Between the ash and lower water levels, freshwater fish are in danger, and so is Arizona’s $691.7 million freshwater fishing industry, the report said. It cited another study, in the scholarly journal Mitigation and Adaptation Strategies for Global Change, that said the U.S. could lose anywhere between $81 million and $6.4 billion by the end of this century because of the impact on freshwater fishing.

Arizona has not seen a major dent in its fishing industry yet, a state official said. The number of fishing licenses issued in the state has generally been steady, although it does drop after major wildfires, said Marc Dahlberg, water quality program manager for the Arizona Game and Fish Department.

The state saw a steep decrease in fishing licenses after the 2002 Rodeo-Chediski Fire and the 2011 Wallow Fire, but that could also have been because some roads were closed, limiting access to fishing spots, Dahlberg said.

Big fires have already taken their toll on fish in Arizona, said Jack Williams, senior scientist at Trout Unlimited. The Apache trout, Arizona’s state fish, was hit especially hard after the Wallow Fire, said Williams, who was part of the Wednesday conference call.

In Colorado, the Poudre River was turned black by ash last year after a wildfire, Inkley said.

“Obviously that’s a problem for those fish species,” he said. “One of the things we can do is reduce the extremity of these forest fires.”

Matt Niemerski, director of Western water policy at conservation group American Rivers, said that there are other problems affecting water levels in Arizona, and climate change is just aggravating them. He said poor planning has put too much demand on the state’s water resources, and the dwindling supply from snowpack is making things worse.

For those reasons, American Rivers named the Colorado River the most endangered river in the country this year.

“Climate change is compounding the interest on our river debt,” Niemerski said. “We already use more than the supply.”

The reason droughts have taken such a toll on communities, Niemerski said, is because they have such a narrow margin between their water supply and consumption. When water levels drop unexpectedly, cities and towns are in the red, water-wise.

“We need to build in some flexibility and resiliency for communities to maintain flow in these rivers going forward,” Niemerski said.

The Apache trout is native to Arizona and is the official state fish. Once endangered, it has enjoyed a comeback, state officials say, but some environmentalists say it has been hit hard by the fallout from wildfires.